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Saturday, 5 September 2015

Leaf Mines

Just a reminder for those of you looking to give your garden year list a late-season boost is that from now until November is the best time of the year to search for larval leaf mines. This is often the easiest way to identify many of our tiniest moth species because most are specific to one particular tree or plant and there are some excellent identification resources available on line, for example at British Leaf-miners and at Dutch Leaf-miners. If you intend to search beyond the confines of your garden I would recommend down-loading and then printing off the mine key on the British site (available here, 43 pages in .pdf format or 35 pages in Word) so that you can take it with you. Of course, the one essential bit of knowledge needed before you start is to be able to correctly recognise the food-plant, but thereafter it should often be fairly easy to come to a species ID by looking at things like the position of the egg, the shape of the mine, the colour and shape of the larva and the way its frass (poo) is distributed within the mine.

Although it is perhaps a week or two early for many species yet, I took a 30-minute look around our own garden at Westcott, Bucks this afternoon to check on what might already be visible and with relative ease found active mines of Stigmella plagicolella (on blackthorn), Stigmella viscerella (on elm), Phyllonorycter leucographella (on pyracantha), Parornix anglicella (on hawthorn) and Parornix finitimella (on blackthorn), as well as numerous vacated mines from the summer generations of other species. If there's a need to study the mines closely I take back-lit photographs like the first two below and then view them on the computer screen.

Mines of Stigmella plagicolella, Westcott 5th September

Mines of Stigmella viscerella, Westcott 5th September

Mine and larva of Parornix finitmella, Westcott 5th September

Nine mines of Stigmella plagicolella on a single blackthorn leaf is probably a record sighting for me and suggests one very lazy female moth! The Parornix blotch mine needed to be opened to get a close view of the larva in order to differentiate it from its close relative Deltaornix torquillella which uses the same food-plant and which I also get in the garden.

...and if you download the key this is made abundantly clear in its introduction. However, most of the mines of other orders are quite different in structure from Lepidoptera mines and are reasonably easy to recognise. Helpfully, many are also illustrated on the websites mentioned.